Re: [PATCH v8 23/38] media: uapi: ccs: Add media bus code for MIPI CCS embedded data

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Hi Laurent,

On Fri, Apr 12, 2024 at 10:07:46PM +0300, Laurent Pinchart wrote:
> Hi Sakari,
> 
> On Thu, Apr 11, 2024 at 09:04:47AM +0000, Sakari Ailus wrote:
> > On Thu, Mar 21, 2024 at 06:49:14PM +0200, Laurent Pinchart wrote:
> > > On Wed, Mar 13, 2024 at 09:25:01AM +0200, Sakari Ailus wrote:
> > > > Add new MIPI CCS embedded data media bus code
> > > > (MEDIA_BUS_FMT_CCS_EMBEDDED).
> > > > 
> > > > Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> > > > ---
> > > >  .../media/v4l/subdev-formats.rst              | 28 +++++++++++++++++++
> > > >  include/uapi/linux/media-bus-format.h         |  3 ++
> > > >  2 files changed, 31 insertions(+)
> > > > 
> > > > diff --git a/Documentation/userspace-api/media/v4l/subdev-formats.rst b/Documentation/userspace-api/media/v4l/subdev-formats.rst
> > > > index cbd475f7cae9..c8f982411e70 100644
> > > > --- a/Documentation/userspace-api/media/v4l/subdev-formats.rst
> > > > +++ b/Documentation/userspace-api/media/v4l/subdev-formats.rst
> > > > @@ -8564,3 +8564,31 @@ and finally the bit number in subscript. "X" indicates a padding bit.
> > > >        - X
> > > >        - X
> > > >        - X
> > > > +
> > > > +.. _MEDIA-BUS-FMT-CCS-EMBEDDED:
> > > > +
> > > > +MIPI CCS Embedded Data Formats
> > > > +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > > > +
> > > > +`MIPI CCS <https://www.mipi.org/specifications/camera-command-set>`_ defines a
> > > > +metadata format for sensor embedded data, which is used to store the register
> > > > +configuration used for capturing a given frame. The format is defined in the CCS
> > > > +specification. The media bus code for this format is
> > > > +``MEDIA_BUS_FMT_CCS_EMBEDDED``.
> > > > +
> > > > +The CCS embedded data format definition includes three levels:
> > > > +
> > > > +1. Padding within CSI-2 bus :ref:`Data unit <media-glossary-data-unit>` as
> > > 
> > > s/Data unit/Data Unit/
> > 
> > Yes.
> > 
> > > > +   documented in the MIPI CCS specification.
> > > > +
> > > > +2. The tagged data format as documented in the MIPI CCS specification.
> > > > +
> > > > +3. Register addresses and register documentation as documented in the MIPI CCS
> > > > +   specification.
> > > > +
> > > > +The format definition shall be used only by devices that fulfill all three
> > > > +levels above.
> > > 
> > > Hmmmm... Do we need to mandate level 3 ? There are lots of sensors that
> > > comply with the first two levels but have their own register set. Would
> > > you like a sensor-specific embedded data format for each of them ? If
> > > so, how would we document it without essentially copying the datasheet ?
> > 
> > You could refer to the datasheet if it's publicly available.
> 
> What if it's not ? How would you expect documentation to be organized ?
> Will we then end up adding one media bus code per sensor ?

Probably. The user space needs a way to find out what to expect. If a
sensor produces its own custom metadata format, it needs to be documented.

There's also documentation for OV2740 embedded data in the set.

-- 
Sakari Ailus




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